The herbicidal activity of 2-(4-(pyridinyl-2-oxy)phenoxy)propionic acids and derivatives thereof is well known in the art; see, for example, U.S. Pat. Nos. 4,046,553, 4,565,568 and 4,753,673. Furthermore, U.S. Pat. No. 4,531,969, for example, teaches that the R-enantiomers of these propionic acids exhibit enhanced herbicidal activity over the corresponding racemates. These same references teach that 2-(4-(pyridinyl-2-oxy)phenoxy)propionic acids and derivatives thereof can be conveniently prepared by reacting substituted 2-halopyridines with 2-(4-hydroxyphenoxy)propionic acid or derivatives thereof under alkaline conditions. The optically active R-enantiomers are similarly prepared by using optically active R-2-(4-hydroxyphenoxy)propionate derivatives. The coupling reaction is generally conducted in a polar aprotic organic solvent such, as, for example, acetonitrile, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) or N-methylpyrrolidinone (NMP).
Although this process generally achieves good yields, it has the disadvantage of using organic solvents which must be separated from the reaction mixture. The separation of the organic solvents from the reaction mixture after formation of the product can require multiple steps and high energy expenditures. After separation, the organic solvents require either waste disposal and/or recycling which often implies elaborate or expensive apparatus. Thus it would be highly desirable to have a process for preparing ((pyridinyloxy)phenoxy)propionate derivatives which eliminates the need of using any solvent.